As the circuit patterns for such microdevices as the semiconductor integrated circuits and others are becoming finer and finer in recent years, the wavelengths of illumination light (radiation) for exposure (exposure light (radiation)) used in the exposure apparatus such as steppers and the like have been decreasing toward shorter wavelengths year after year. Namely, as the exposure light, KrF excimer laser light (wavelength: 248 nm) is going mainstream in place of the i-line (wavelength: 365 nm) of mercury lamps mainly used conventionally, and ArF excimer laser light of a much shorter wavelength (wavelength: 193 nm) is also nearing practical use. For the purpose of further decreasing the wavelength of the exposure light, there are also attempts to use halogen molecular lasers and others like the F2 laser (wavelength: 157 nm).
Although the aforementioned excimer lasers, halogen molecular lasers, etc. are available as light sources in the vacuum ultraviolet region of wavelengths not more than 200 nm, there are limits to practical band narrowing thereof.
Since limited materials transmit the emitted light in this vacuum ultraviolet region, available materials are limited for lens elements constituting the projection optical systems and transmittances of the limited materials are not so high, either. As matters now stand, the performance of antireflection coats provided on surfaces of the lens elements is not so high, as against those for longer wavelengths.
A first object of the present invention is to suppress chromatic aberration of the projection optical system and reduce loads on the light source.
A second object of the present invention is to correct chromatic aberration for the exposure light having some spectral width, by adding a single kind of glass material or a few color-correcting glass materials.
A third object of the present invention is to obtain an extremely fine microdevice circuit pattern while simplifying the structure of the projection optical system.
A fourth object of the present invention is to obtain an extremely fine microdevice circuit pattern without decrease in throughput.